Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C1/00—Ingredients generally applicable to manufacture of glasses, glazes, or vitreous enamels
  • C03C1/02—Pretreated ingredients
  • C03C1/026—Pelletisation or prereacting of powdered raw materials
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B1/00—Preparing the batches
  • C03B1/02—Compacting the glass batches, e.g. pelletising
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C1/00—Ingredients generally applicable to manufacture of glasses, glazes, or vitreous enamels
  • C03C1/002—Use of waste materials, e.g. slags
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping

Definitions

• the subject of the invention is a method of glass batch pelletizing with the use of activated cullet.
• the method is suitable for pelletizing of batches applicable to melting of soda-lime container, float, lighting, and tableware glasses, as well as to borosilicate C-type for glass wool and E-type for continuous glass fibre production.
• the article of E. Alvarez Ayuso i H. Nygteren Reduction of alkaline waste streams from anodising industry by production of dawsonite describes a mechanism of waste sodium aluminate formation during aluminium etching in mixed solution of sodium hydroxide and sodium aluminate as a first step of aluminium anodisation process. As a solution being continuously saturated in aluminium it becomes waste, unfit for subsequent use.
• Effluents from aluminium etching process typically contain: 132 g/l of Al and 151 g/l of Na on average.
• Effluents from first rinse contain: 67 g/l of Al and 71 g/l of Na on average.
• US 3914364 describes a batch pelletizing method based on disc pelletizer application, where premixed batch containing up to 15% of lime fraction of grain size below 0,08 mm (325 mesh), and/or 25% of dolomite fraction of grain size below 0,128 mm (200 mesh) is mixed with water solution of NaOH of 40-73% concentration in amount up to 15% on total batch basis.
• US 4026691 describes a batch pelletizing method where the slurry obtained by reaction of NaOH with part of limestone and/or dolomite at 80 -160°C is added to remaining glass batch materials during pelletizing on disc pelletizer.
• US 4028131 describes the method of batch preparation suitable for pelletizing, characteristic in mixing of sand with quicklime and/or calcined dolomite with caustic soda with or without alkali metal salts.
• US 4031175 describes a process of batch ingredients pelletizing in disc pelletizer using concentrated solution of alkali metal hydroxide as binding agent.
• the innovation consists in using at least 20% of fine dolomite below 0,25 mm (100 mesh) and 15% of fine limestone below 0,128 mm (200 mesh).
• US 4235618 describes a process of borosilicate glass batch pelletizing. In order to minimize the sticky or tacky surface characteristic of free water containing pellets, the fresh pellets are additionally covered with dry batch.
• US 4252754 describes a treatment of pellets obtained by using NaOH as binding agent with hot waste gases from a glass melting furnace.
• Polish patent PL 111274 describes a pelletizing method of glass batch using 10-30% of glass powder of average size 0,1- 2,5 mm with chemical composition compatible with the batch.
• As a binding agent water glass solution in water is used in ratio from 1:2 to 1:5, in 8-15% of volume.
• US 4349366 describes a continuous pelletizing process in a drum pelletizer. Green granules containing 4-12 % of water are used as nuclei for new pellets. During the pelletizing process, sand, lime and NaOH are added in sequence.
• a binding effect is additionally forced due to calcium and/or magnesium hydroxide formed "in-situ" as a product of sodium hydroxide with lime and/or dolomite. This effect is stronger when using the method described in US 4026691 , where the reaction proceeds at an elevated temperature.
• EP 1966105 describes the application of the attritor for forced silicate substance activation in order to obtain multifunctional additive lowering density and setting time of the cement containing mixture.
• This additive could be used as slurry, powder or agglomerate to initiate a hardening process of mixtures with other materials, without the necessity of hydrothermal conditions.
• Polish patent application P.408208 presents a method of binder preparation in two-stage geopolymerization of blast furnace fine slag of average grain size below 10 ⁇ m in a solution of water glass and sodium aluminate.
• Glass batch pelletizing methods known from patent literature are primarily based on water glass or sodium hydroxide addition to raw materials during mixer blending. Thin films of viscous liquid are formed on a surface of grains of raw materials, which promote their aggregation during pelletizing process more often performed on disc device. Mixing time rarely exceeds 6 minutes and is too short to give any important progress of chemical reaction between alkali silicate or alkali hydroxide with sand or feldspar grains in the batch. Chemical affinity of batch components to this kind of binding agent promotes only better grains wettability by binding liquid. Consequently, to obtain the aggregating effect based on adhesion forces, addition of 5 to 8 % of water glass is required, making such a pelletizing process unprofitable for glasses mass produced as container or float glasses.
• binding agent A far bigger volume of binding agent could be obtained with the same water glass quantity if, instead of simple introduction into a mixer, the binding agent is applied as alkaline activator of slag or fly ash.
• Polish patent application no P.408208 describes a method of preparation of effective binder proceeding in two-step geopolymerization supported by sodium aluminate addition, suitable for glass batch granulation.
• the binding agent is not water glass, but the product of its reaction with fine milled granulated blast furnace slag with average grain size below 10 ⁇ m or quicklime and sodium aluminate.
• Binder is added to the rest of batch raw materials excluding soda ash, which is introduced at the end of the mixing process. This method required a long time and a costly additional milling process of commercially available fine slag with typical average grain size below 100 ⁇ m.
• This invention is aimed at the preparation of a universal method of glass batch pelletizing suitable for any glass factory that uses own or external cullet.
• the object of the invention is a method of glass batch pelletizing with binding agent obtained as a product of cullet activation, proceeding in two steps:
• the binding agent obtained according to the above method is mixed with the rest of glass batch components and after that, a pelletizing is undertaken without any delay, while continuously proceeding polycondensation of hydrated aluminosilcate gives required mechanical strength and thermal resistance of obtained pellets. Due to these properties, pelletized batch is suitable for transportation, storage, and preheating with hot flue gases from a glass-melting tank.
• the procedure of alkali activation according to the present invention utilizes a dualism of function that cullet and slag could play in pelletized glass batch.
• cullet and slag could play in pelletized glass batch.
• they could be ordinary raw material bearing oxides such as SiO 2 , Al 2 O 3 , CaO, MgO, Na 2 O and K 2 O to glass.
• they could be amorphous or partly amorphous aluminosilicate precursors of binding agent.
• Cullet in the first role should preferably be sized from 3 to 50 mm and slag sized from 0,1 to 1 mm. Fly ashes are rather rarely used as a glass batch component, but by definition their size is below 100 ⁇ m.
• three properties of cullet, slag and fly ash, or their mixture are important: availability of the required binder quantity based on highest limits of cullet, slag or fly ash in the specific glass batch, suitable chemical and phase composition of products after dissolution in water glass, and time required to achieve binder enable to compact whole batch grains during the mixing and pelletizing operation.
• Cullet and/or slag and/or fly ash used as binding agent precursor should be characterized by an appropriate grain size distribution, wherein the upper limit for cullet is 3 mm, for slag 1 mm, and for fly ash 0,1 mm.
• the best choice is, of course, to use commercially available products. Considering granulated blast furnace slag, there are raw materials available on the market matching glass melting process requirements. In the case of own cullet, the fraction passing through a 3 mm sieve is the preferred choice for a binding agent precursor.
• the use of very fine precursors, cullet and/or slag and/or fly ash of grain size below 100 ⁇ m guarantees that all three above-described criteria could be fulfilled.
• the method of preparing binding agent based on fast geopolymerization of sols of hydrated aluminosilicates obtained by alkali activation of soda-lime glass cullet solves the problem of application of this approach to flint glass, among them, extra white flint, where use of slag is substantially restricted.
• Sodium and/or potassium silicates used for partial dissolution of aluminosilicate precursor prior to application are diluted with water in the amount of 5 - 25% of total mass of entire batch components.
• single or multicomponent aluminosilicate precursor is introduced into a wet milling device, such as ball mill or attritor, equipped with pan and balls made from material resistant to alkaline corrosion, and subjected to activation mechanically and thermally boosted for 5 to 180 minutes.
• a wet milling device such as ball mill or attritor
• pan and balls made from material resistant to alkaline corrosion
• activation mechanically and thermally boosted for 5 to 180 minutes is preferable.
• coarse cullet as a grinding medium is preferable.
• the slurry is screened on a 3 mm sieve in order to separate binding agent from grinding medium.
• a second step of binding agent preparation according to the invention is forced partial substitution of [SiO n (OH)( 4-n )] n- groups in hydrated silicates and aluminosilicates of calcium and/or magnesium and/or sodium and or potassium by [AlO n (OH) (4-n) ] (n+1)- ⁇ (n+1)Na + groups coming from sodium aluminate solution of Al 2 O 3 /Na 2 O module from 0,5 to 1,0 and concentration of oxide Al 2 O 3 +Na 2 O sum from 5 to 50%, taken in the amount corresponding to the ratio of Al from sodium aluminate to Si from sodium and/or potassium silicate from 0,05 to 1.
• a polycondensation of obtained hydrated aluminosilicates of calcium and/or magnesium, sodium and/or potassium is carried out by additional stirring of the slurry for 1 to 30 minutes.
• the starting quantity of cullet or mixture of cullet with slag and/or fly ash is selected according to the rate of precursor dissolution progress measured by concentration of calcium and/or magnesium and/or sodium and/or potassium silicates and alumininosilicates monomers and oligomers. Only the volume and composition of binder are important when considering the relation of binding agent with pelletizing process efficiency. Precursor's grain size at the beginning and end of the process is of negligible importance, as even presence of cullet and/or slag and/or fly ash grains of starting dimension, meaning respectively 3, 1 and 0,1 mm, is not a problem because they are useful batch components, additionally functioning as nuclei of aggregated pellets.
• the only important criteria is the concentration of calcium and/or magnesium and/or sodium and/or potassium silicates and alumininosilicates monomers and oligomers obtained at the end of cullet and/or slag and/or ash dissolution, which after addition of sodium aluminate give a sufficient amount of binding agent to aggregate all raw materials into pellets.
• the use of sodium aluminate is crucial for obtaining binding agent prone to polycondensation based on a formation of Al-O-Si bonds within a reasonable timeframe.
• Obtained binder is mixed with all raw materials comprising batch for 1 to 10 minutes and transferred without any delay to a pelletizing device of any construction, preferably drum or centrifugal.
• cullet as a precursor of binding agent and its wet grinding in water glass solution as a preparation method enables the application of water glass of higher module value than when the binder is obtained as a result of stirring of finely ground slag with water glass and sodium aluminate.
• the upper limit could be shifted from 2,6 to 3,6.
• Products of cullet dissolution act as an additional source of alkali, consequently the conditions required for forming the hydrated polyaluminosilicates of calcium and/or magnesium and sodium and/or potassium with water glass of modules from 2,5 to 3,6 are provided. It is important for two reasons: 1) water glass of module 3,6 is two times cheaper than water glass of module 1,7 and 2) water glass of higher module are more safe during handling due to a lower pH value.
• An aluminium deficit in cullet and slag of specific origin, important for polycondensation rate, is compensated by the addition of sodium aluminate.
• the method disclosed in this invention also provides the solution for a cheap, effective binding agent suitable for pelletizing batches for glass of high transparency.
• own cullet is used as a binder precursor.
• the finest fraction of recycled cullet and slag, or their mixture are sources at disposal.
• the finest fraction of cullet being a source of undesirable foam on glass melt surface in the charging area, is difficult for reuse in the melting technology currently used.
• Procedure of binding agent preparation during wet grinding of a precursor in alkaline activator has three important advantages: 1) energy requirements are limited to a minimum, 2) heat released during grinding increase amount of binder without extending time of the process and 3) undissolved precursor's grains, in case of cullet below 3 mm and in case of slag below 1 mm, are used as pellet nuclei, additionally increasing their mechanical strength. Grinding parameters are optimised every time according to the precursor characteristic and expected precursor's volume and composition. For example, when cullet is also used as a grinding medium and part of it is in a form of pieces bigger than 3 mm, mill is discharged through a 3 mm screen and filled with next portions of cullet, water, water glass and sodium aluminate. The stability of binding agent composition is checked by density and pH index measurements.
• Optimal pellets granulation depends on the kind of glass and the method of charging batch to a furnace.
• their size distribution should guarantee highest heat transfer and smallest flue gas pressure drop between inlet and outlet simultaneously.
• values of effective heat conductivity of pellets are 10 times higher at 250°C and 4,5 times higher at 500°C than for loose dusty batch, they are still twice lower than for cullet. For this reason, to assure uniform pellet preheating without a pressure drop, the biggest ones should not cross the 12 mm diameter limit. To minimise danger of dust carryover with flue gases, smallest pellets should be over 2 mm.
• the pellets' grain distribution should make them resistant to carryover from flame velocity and pressure changes inside the furnace combustion space.
• the lowest limit for this case is 1,6 mm.
• the highest limit is defined by temperature equalization rate in batch layer in batch charging area. Because it is advantageous to keep the same step of chemical reaction across whole batch layer height, the dominant grain size fraction of pellets should be kept in 4 to 10 mm range.
• Such granulation also gives conditions promoting easy CO 2 release from the MgCO 3 part of dolomite and in some extends also from CaCO 3 before the first liquid appears. Depletion of glass melt in dissolved gas and bubbles gives conditions for shortening a fining time and lowering hot spot temperature in the furnace.
• waste product in the form of sodium aluminate originating from aluminate etching before anodisation.
• the core of the presented invention is also the use of own or external cullet or cullet in mixture with blast furnace slag or fly ash, where the first step of alkaline activation is performed in a way that fulfils at least one of the following three conditions: 1) continuous increase of reaction's surface, 2) increased reaction's temperature and 3) continuous removal of product's layer from precursor's grains that means alkali activation is thermally and mechanically boosted, and the second step in a way that fulfils the conditions for forced substitutions of [SiO n (OH) (4-n) ] n- groups in silicates and aluminosilicates of calcium and/or magnesium and sodium and/or potassium with [AlO n (OH) (4-n) ] (n+1)- ⁇ (n+1)Na + groups from sodium aluminate.
• a separate glass category comprises borosilicate glasses, especially E type. Due to hard melting conditions, batches for E glass are composed of finely ground raw materials, typically below 60 ⁇ m. In this case, the pelletizing process solves the problem of dust emission during batch transportation, charging and carryover inside the furnace, which is the main source of refractory corrosion in the furnace superstructure.
• the invention solves a few important problems related to glass melting and simultaneously proposes the use of two waste materials which, until now, had no important industrial application: finest fraction of cullet, and waste sodium aluminate from aluminium etching before anodisation. Moreover, the invention solves a few important issues related to the glass melting process. Using batches pelletized according to the method in the invention allows the decrease of dust emission to the atmosphere during transportation, charging and melting, faster reactions rates, and improved glass quality. In pelletized batches used for melting, important drawbacks of loose batches are eliminated: segregation tendency and long lasting fining process. These advantages give rise to three opportunities for the furnace operator: 1) decrease of energy consumption with the same glass output, 2) decrease of hot spot temperature with the same glass output and 3) output increase with the same energy consumption. Batches prepared according to this invention are ready for preheating with flue gases from the melting furnace.
• waste E-glass of composition in wt. % 55,05 SiO 2 , 12,05 Al 2 O 3 , 7,6 B 2 O 3 , 21,5 CaO, 2,0 MgO, 0,15 SrO, 0,8 Na 2 O, 0,2 K 2 O, 0,2 Fe 2 O 3 , 0,1 TiO 2 , 0,35 SO 3 of average diameter 50 ⁇ m and 65 g of granulated blast furnace slag of composition in wt.

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Cited By (3)

Citations (12)

• 2015
  • 2015-05-19 EP EP15020076.4A patent/EP3095765A1/fr not_active Withdrawn

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